1. Technical Field of the Invention
The present invention relates to telecommunications networks. More particularly, but not by way of any limitation, the present invention relates to a congestion control mechanism for use with an access multiplexer disposed in an access network portion of a telecommunications network, wherein the access multiplexer receives message flows from the network and a plurality of users.
2. Description of Related Art
The remote access market is undergoing a major metamorphosis. Three factors serve as catalysts for change. The first is the growing number of users, for example, small office/home office (SOHO) users, demanding high performance Internet and remote access for multimedia. The second factor is the Telecommunications Reform Act, which is fostering broader competition through deregulation. The third and final factor is congestion in the Public Switched Telephone Network (PSTN), originally designed and developed for voice-only traffic.
There have been several important advances in telecommunications technology that enable high rates of throughput in carrier networks backbone connections. For example, by implementing Asynchronous Transfer Mode (ATM) networking technology over a Synchronous Optical Network (SONET)/Synchronous Digital Hierarchy (SDH) physical layer, carrier networks can achieve data rates of up to several hundred megabits per second (Mbps). However, efforts to meet the bandwidth demand for remote access are beset by the limitations of the existing twisted-pair copper cable infrastructure provided between a carrier""s central office (CO) and a subscriber""s remote site, typically referred to as the local loop. In the telecommunications art, these limitations are sometimes collectively described as the xe2x80x9clast-milexe2x80x9d problem.
Current advances in technology are making it possible to get more bandwidth from the existing twisted-pair copper cable infrastructure. One of these developments is the Digital Subscriber Line (DSL) technology which utilizes the local loop telephone wiring already installed to virtually every home and business in the world, but does not depend on the rest of the PSTN infrastructure.
DSL is a modem technology for converting existing twisted-pair telephone lines into access paths for multimedia and high-speed data communications. Some versions of this technology are asymmetric, with different data rates in the downstream and upstream directions (to and from the subscriber, respectively). Others are symmetric, providing the same data rate both upstream and downstream. Regardless of the version, DSL technology provides three distinct advantages: (i) separation of voice and data communications, (ii) ability to implement the technology incrementally and inexpensively, and (iii) effective utilization of the open market place created by local loop deregulation.
An Asymmetric Digital Subscriber Line (ADSL) circuit connects an ADSL modem on each end of a twisted-pair telephone line, creating three information channelsxe2x80x94a high speed downstream channel, a medium speed duplex channel, and depending on the implementation of the ADSL architecture, a Plain Old Telephone Service (POTS ) or an Integrated Services Digital Network (ISDN) channel. The POTS/ISDN channel is split off from the digital modem by filters, thus guaranteeing uninterrupted POTS/ISDN connectivity, even if ADSL fails. The high speed channel ranges from 1.5 to 6.1 Mbps of throughput, while duplex rates range from 16 to 640 kilobits per second (Kbps).
With the deployment of DSL technologies for remote access, it is now possible to establish end-to-end broadband connectivity over packet-switched networks such as ATM networks. As is well known, one of the characteristics of ATM networks is that they are connection-oriented, that is, before two end systems can communicate they need to establish a connection between them. However, unlike circuit-switched networks (e.g., the Public Switched Telephone Network or PSTN), the connection between the two end points does not consume a fixed bandwidth. Instead, bandwidth is allocated statistically, so that a large number of connections can share the bandwidth of individual links in the network. Since these connections are not dedicated bandwidth channels, they are typically referred to as xe2x80x9cvirtual channel connectionsxe2x80x9d (VCCs) or xe2x80x9cvirtual circuitsxe2x80x9d (VCs).
VCCs between two ATM endpoints can be established in one of two ways. In the provisioning method, the virtual circuits are permanently configured and left in place until the subscribers want them to be removed. Accordingly, such circuits are known as permanent virtual circuits (PVCs). Typically, no special signaling protocol is necessary to handle control signaling (e.g., set-up and tear-down) of the PVCs. On the other hand, virtual circuits can also be established on demand and such circuits are called switched virtual circuits (SVCs). These SVCs are created and destroyed dynamically as needed and, accordingly, require a signaling protocol for exchanging messages necessary to set up and tear down SVC connections. Such a protocol, known as Service Specific Connection Oriented Protocol (SSCOP) has been specified in the ATM Adaptation Layer (AAL) for effectuating the Broadband ISDN (B-ISDN) signaling architecture in ATM networks. The SSCOP is defined by the ITU as ITU-T Recommendation Q.2110 and is incorporated by reference herein.
The SSCOP provides connection control and governs the message transmission process between a receiver and a transmitter disposed in an SVC. In the context of the ADSL technology, an access multiplexerxe2x80x94which is provided as a node that concentrates a plurality of ADSL lines from users (i.e., customer premises equipment or CPE) and is coupled to the carrier network via a Point of Presence (POP) switchxe2x80x94operates as an SSCOP receiver for traffic emanating from the users as well as the network itself.
Those skilled in the art should appreciate that the access multiplexer node can experience heavy amounts of signaling traffic from the users, the network, or both, and, accordingly, its resources (i.e., processor resources, buffer availability, etc.) may become overloaded. Although the SSCOP provides a flow control mechanism by way of a credit window that is granted by the receiver to the transmitter, there are certain deficiencies and drawbacks associated therewith.
First, the SSCOP Recommendation does not specify how the credit window needs to be managed by the receiver when the receiver experiences traffic overload, i.e., congestion. While the receiver can update a message sequence indicator that is transmitted back to the transmitter to indicate the highest number of messages it can accept, the Recommendation provides that the updating procedure is implementation-specific and not subject to standardization. Accordingly, there is a need to address the issue of credit window management in the context of congestion in a receiver.
Second, the SSCOP treats every call or user equivalently without taking into account whether some users/calls use up the resources more rapidly than others. In other words, some users may be sending message packets fast enough to tie up the resources unfairly. Accordingly, the resources of a receiver may be overloaded due to an imbalance of the loading itself, and the SSCOP does have any precautions against such unequal use patterns.
Based on the foregoing, it should be apparent that in order to address these and other problems of the state of the art set forth above, what is needed is a congestion control solution for use with receivers operating a communication protocol such as the SSCOP that advantageously offers a mechanism for throttling message flows from transmitters based on the overload conditions. It would be of further advantage to provide a congestion control method that is capable of isolating malfunctioning users by restricting their credit window sizes. The present invention provides such a solution.
Accordingly, the present invention advantageously provides a congestion control mechanism for a Digital Subscriber Line Access Multiplexer (DSLAM) module (also referred to as an ADSL Access Multiplexer (ASAM) module) wherein message flows from transmitters (either a network portion or a plurality of CPE units) are monitored with respect to buffer usage in the DSLAM module and when certain buffer use counters reach predetermined values, an indication is provided to the transmitters such that their message transmit windows are dynamically controlled. The message flow emanating from the transmitter that consumes buffers rapidly in the receiver, i.e., the DSLAM module, is consequently throttled so as to reduce congestion in the receiver.
In one aspect, the present invention is directed to a congestion control method for managing message flow between a transmitter and a receiver disposed in a telecommunications network. The method commences by initializing, in the receiver, a buffer count variable associated with a common buffer pool (CBP) allocated for effectuating a communication protocol in the receiver. When messages from the transmitter are received in the receiver, the buffer count variable associated with the CBP is decremented appropriately. The receiver maintains a message sequence indicator that is transmitted back to the transmitter to indicate the next message in the sequence that the receiver can accept (i.e., the transmit window of the transmitter). When the buffer counter variable is above a select minimum value, the receiver updates the message sequence indicator and transmits it to the transmitter. When the buffer counter variable reaches the minimum value, the message sequence indicator is not incremented (i.e., it is held constant) until the buffer counter variable associated with the CBP attains a predetermined threshold value due to buffer releases, etc. Thereafter, the message sequence indicator in the receiver is updated normally in response to the messages received from the transmitter. Consequently, by throttling the updating of the message sequence indicator which is transmitted from the receiver to the transmitter, the message transmit window associated with the transmitter is dynamically controlled.
In another aspect, the present invention is directed to a congestion control method for throttling message flows emanating from a plurality of users (i.e., CPEs coupled with User-Network Interfaces or UNIs). A DSLAM module is provided as a receiver in an access network portion of the telecommunications network. The congestion control method begins by initializing, in the receiver, a buffer credit pool for each CPE unit, wherein the buffer credit pool corresponds to a maximum number of messages that may be transmitted by a CPE unit in a first select time period. The buffer credit pool is decremented responsive to the messages received in the receiver from a select CPE unit corresponding thereto. If the number of messages transmitted from the select CPE unit remains below its buffer credit pool, a message sequence indicator in the receiver is incremented responsive to the messages sent by the select CPE unit until the buffer credit pool is re-initialized by the receiver at the expiration of the first select time period. Otherwise, if the messages transmitted from the select CPE unit exhaust the buffer credit pool therefor, the message sequence indicator is incremented by an iterative variable for every second select time period, until the iterative variable reaches a maximum value. Thereafter, the buffer credit pool is reinitialized by the receiver at the expiration of the first select time period. The congestion control method transmits back the message sequence indicator from the receiver to each CPE unit so as to dynamically control its message transmit window.
In a presently preferred exemplary embodiment of the present invention, the messages are transmitted from the telecommunications network over an Access Network Interface (ANI) disposed between the DSLAM and the network, or from the CPEs over UNIs, and relate to the control signaling of Service Specific Connection Oriented Protocol (SSCOP) for effectuating the Signaling ATM Adaptation Layer (SAAL) standard.
In yet further aspect, the present invention is directed to a congestion control system for use in a DSLAM module disposed between a distribution channel portion and an aggregate channel portion of a telecommunications network. The DSLAM module receives messages from the aggregate channel portion over an ANI and from a plurality of CPE units over UNIs in the distribution channel portion. The DSLAM module is provided with a common buffer pool of a plurality of buffers for effectuating a communication protocol therein. The congestion control system comprises a structure for monitoring incoming messages over the ANI and the UNIs, wherein the incoming messages consume the plurality of buffers in a predetermined fashion. A message sequence indicator is provided in the congestion control system for indicating to a transmitter to decrease the transmitter""s transmit window when a variable associated with available common buffer pool reaches a select value. The transmitter may comprise the aggregate channel portion of the telecommunications network or one of the CPE units. A structure is provided to update the message sequence indicator when messages are received in the DSLAM, wherein the updating structure includes a buffer use counter for messages received over the ANI and a plurality of credit counters associated with messages received over the UNIs. The message sequence indicator is updated based on the contents of the buffer use counter or the plurality of credit counters.